Is this letter from Colorado Department of Revenue, that is aking me to validate my return, legit?

[CarolynM]

Perhaps. Many states have increased their security measures to protect against identity theft and mailing these types of letters.

To make sure the letter really is from the Colorado Department of Revenue, confirm the address on the letter you received matches the agency.

Here is a link to the various agency addresses: https://www.colorado.gov/pacific/tax/mail-form

and the street address is: 1375 Sherman St, Denver, CO 80203